<?php
/**
 * Update the featured images size from Astra
 */
add_filter( 'astra_post_thumbnail_default_size', 'update_featured_images_size_callback' );

function update_featured_images_size_callback( $size ) {
    $size = array( 500, 500 ); // Update the 500(Width), 500(Height) as per your requirment.
	return $size;
}